Abstract: The geological sample was decomposed by aqua regia and suitable amount of triethanolamine (TEA) sensitizer was added in the sample solution. Molybdenum in the sample was then determined by airacetylene flame atomic absorption spectrometry. The dosage of triethanolamine was optimized through experiments. The characteristic concentration of molybdenum in four different kinds of media including HCl-H3PO4-AlCl3, HCl-TEA, HCl-TEA-H3PO4 and HCl-TEA-H3PO4-AlCl3was investigated. The results showed that in the HCl-TEA-H3PO4-AlCl3 medium, a wide dynamic linear range was obtained with Mo concentration up to 40 μg/mL. The detection limit of this method is 0.2 mg/L for Mo. The recovery of standard addition is 96%～102% with precision of 5.6%RSD（n=6）. The method has been applied to the determination of Mo in national primary standard reference materials and the results are in good agreement with the certified values.